Forty percent of 18-25 year olds are overweight or obese, yet this population is also markedly under- represented in standard behavioral weight loss (BWL) programs and to date, no fully powered trials exist which target this age group for weight loss. Formative work conducted with this age group revealed that existing BWL programs do not meet their unique needs, and also identified lack of motivation as a fundamental barrier for weight management. The primary aim of this proposal is to test the relative efficacy of two novel, low intensity web-based approaches to weight loss in this age group that are specifically focused on enhancing motivation, relative to a standard web-based program. We recently pilot tested these two approaches with promising results. Both 3-month intervention programs consisted of a single group based session, followed by a web- based program with weekly lessons, a self-monitoring platform and personalized feedback. One program was rooted in Self-Determination Theory and designed to facilitate intrinsic motivation and promote autonomous self-regulation by offering a variety of personal choices in the treatment program and emphasizing autonomy around behavioral goals and in weekly feedback. The other intervention was grounded in learning theory and principles of behavioral economics, and offered small financial incentives for meeting self-monitoring goals; further, participants achieving a clinically significant weight loss were entered into a raffle for additionl monetary incentives. Preliminary data for both approaches are quite promising - engagement and retention were strong, and participants achieved clinically significant weight losses at 3 months (ITT=4.8% in the Autonomous Motivation program and 8.8% in the Extrinsic Motivation program). Moreover, weight losses were maintained at 6 months without any additional contact (5.1% and 10.1%, respectively). We propose a 3-arm randomized controlled trial to test the longer-term efficacy of these novel approaches to weight loss in this high risk population. Participants will be 381 young adults, 18-25 years, with a body mass index (BMI) of 25-45 kg/m2, who will be randomized to 1 of 3 arms: 1) Standard Web BWL (Web), 2) Web + Autonomous Motivation (Web+Aut), or 3) Web + Extrinsic Motivation (Web+Ext). All arms will receive a 6-month program followed by a 6-month no-contact follow-up period. Motivation will be assessed at week 2 and months 2, 4, and 6. Assessments of weight and secondary outcomes will occur at 0, 3, 6, and 12 months. We will compare treatment effects across all three arms at 6 months, and compare arms on weight loss maintenance from 6 to 12 months. We will also examine mediators of treatment outcomes consistent with our theoretical framework (i.e. autonomous motivation, extrinsic motivation). We hypothesize that the Web+Aut and the Web+Ext conditions will produce greater weight loss and improvement in secondary outcomes at 6 months, compared with Web. We further hypothesize that Web+Ext will achieve greater weight loss and improvement in secondary outcomes at 6 months, relative to Web+Aut.